1. Field of the Invention
The present invention relates to an automatic belt tightener and more particularly to a belt drive mechanism for transmitting torque between a driving rotatable member and a driven rotatable member thereby making use of such an automatic belt tightener for insuring efficient transfer of torque between the driving member and the driven member and further, for automatically taking up any slack that may be present in such a belt drive arrangement.
2. Description of the Prior Art
The rotational velocity of an element being rotated, such as the drum of a domestic clothes dryer, is often times critical and is necessary to be kept within given small tolerances in order to maintain the proper tumbling of clothes in the drum. This is especially so since the outside diameter or surface of the dryer tumbling drum is commonly used as a large pulley. However, in converting from the use of a four-pole drive motor rotating at 1725 RPM's to a two-pole drive motor rotating at 3450 RPM's, in order to maintain this fixed rotational velocity it is necessary to halve the diameter of the motor drive pulley; that is, when the drive pulley of the four-pole motor was 5/8" diameter, it is necessary to convert to a 5/16" diameter when using a two-pole motor. A problem arises, that of poor driving engagement between the motor drive pulley and the drive belt due to reduced frictional surface. In fact, a two-pole motor having a 5/16" diameter drive pulley turning at 3450 RPM's is virtually unable to transmit full torque without external help and instead causes over-heating and subsequent destruction of the belt.
Prior art such as U.S. Pat. No. 2,243,538-Salfisberg shows a device for providing pressure between a belt and a driving pulley independent of tension in the belt and independent of any take-up device that is ordinarily used to regulate that tension. Salfisberg U.S. Pat. No. 2,243,538 shows a set of three pulleys, the pressure exerted against the belt being manually adjustable by varying air pressure in a pneumatic drive pulley. It is, however, desirable that such frictional engagement between the belt and the driving member be applied automatically by the device itself.
Furthermore, in production application, a tolerance is necessary in belt lengths; and means, preferably automatic, must be provided for taking up the slack that may result in a belt drive system due to this tolerance. Also, with use and age, the belt tends to lengthen and it is desirable that means should be provided for automatically taking up the slack that results.
The prior art has taught the use of idler roller tensioners which are usually spring loaded to effect this operation. One such application is shown in U.S. Pat. No. 3,211,015-Bochan, assigned to the same assignee as the present invention.
The prior art also teaches an automatic belt tightener mechanism in U.S. Pat. No. 3,864,986-Bochan, assigned to the same assignee as the present invention. That mechanism takes up the belt slack and increases the frictional drive engagement automatically and eliminates the need for idler roller tensioners. That mechanism, however, drives the belt about a small diameter motor drive pulley and has the belt pinched between the driver and the pulleys or rollers which can detrimentally affect the belt wear and life.
By the present invention, there is provided an automatic belt tightener that solves the above-mentioned problems and which is highly reliable, efficient and of low-cost.